(1) Field of the Invention
The present invention pertain""s to fans of the type mounted on the shafts of electric motors and other similar dynamoelectric devices for cooling such devices during operation. More specifically, the present invention pertains to a radial fan having two sets of blades on axially opposite sides of the fan. On rotation of the fan, the first set of blades draws air in a first direction axially toward the center of the fan and then pushes the air radially outward which then is redirected axially by an end shield over the exterior of the fan, motor, thereby cooling the exterior of the motor stator. Also on rotation of the fan, the second set of blades draws a flow of air in a second, opposite direction axially toward the center of the fan through the stator, thereby cooling the stator windings. The second set of blades then redirects the airflow back over the exterior of the stator assisting in the cooling of the stator exterior. The two sets of blades on the axially opposite sides of the fan improve its cooling efficiency without increasing its size, thereby providing a greater cooling capacity over conventional radial fans of the same size.
(2) Description of the Related Art
Many dynamoelectric devices such as appliance motors for dishwashers, clothes washers and whirlpool baths utilize fans mounted on their rotor shafts to provide for air cooling of the stators and the rotors of the motors during their operation. Typically, such a fan is mounted internally at one axial end of the electric motor and is configured to pull or push air through the housing of the motor between the rotor and stator, thereby cooling the motor. The fan can also be mounted on the shaft of the motor outside the motor housing and is covered by a fan shield. On operation of the motor, rotation of the fan draws air into the fan shield and then pushes the air radially outward. The fan shield then redirects the flow of air axially over the exterior of the motor.
A typical electric motor is generally cylindrical in shape and its fan is commonly configured to have nearly the same diameter as the device housing. It is also common for the motor to have a cover enclosing the fan, or to place the fan within the housing of the motor to prevent objects from contacting the fan blades.
Additionally, it is generally desirable to configure the cooling fan in a manner such that it takes only a minimum of space so that it can fit compactly within the housing of the motor.
Many machines in which electric motors operate allow for the use of axial flow fans. However, the configurations of many machines in which electric motors are used often necessitate the use of radial flow fans which discharge air radially outward. Radial flow fans are designed to obtain maximum air flow rates for a given configuration. Other design considerations for the use of radial flow fans include costs and whether the fan must operate in opposite directions of rotation.
One of the simplest radial flow fan designs is a straight blade fan. Straight blade fans utilize a plurality of blades that extend radially outward from a central motor shaft hub of the fan. Like other fan designs, the hub is typically a cylindrical body having a through hole for mounting the fan to the shaft of a dynamoelectric device. The blades of a straight blade radial fan are typically flat, rectangular members oriented parallel to the axis of rotation of the fan so that they will push air radially outward from the fan purely by centrifugal force. The fans are typically mounted on the shaft of the dynamoelectric device at one axial end of the shaft and draw or push air through the axially opposite end of the device on rotation of the fan. The air drawn through the device cools its stator as the air is drawn to the fan at the opposite end of the device. The cooling air is then pushed radially outward from the device housing by the fan. To reduce the amount of air drawn into the radial fan from the side of the device housing at which the fan is mounted, radial fans often have a disc shaped backing wall that rotates with the blades of the fan and blocks the flow of air into the fan from the side of the device at which the fan is mounted. In this way the backing wall increases the amount of air drawn into the device housing from the end of the housing axially opposite the fan. Generally, straight blade radial fans produce a greater air flow rate than axial flow fans or other types of fans, for example backward curved blade fans of the same size. For this reason, straight blade radial fans are desirable for use in cooling most dynamoelectric devices.
Although radial flow fans have proven effective for cooling dynamoelectric devices, it remains advantageous to design fans having ever greater efficiency. Furthermore, it is desirable to increase the cooling efficiency or motor cooling ability of such fans without increasing the size of the fans and without significantly increasing the cost or adding additional components to the dynamoelectric device assembly.
The radial fan of the present invention increases the flow rate of cooling air through a dynamoelectric device with which it is used as compared to prior art straight blade radial fans of the same size. The increased air flow is a result of the fan being comprised of two sets of blades that are positioned on axially opposite sides of a center plate of the fan, as well as the configuration of an annular ring joining the distal ends of one set of blades.
The fan of the preferred embodiment of the invention is designed for use with a dynamoelectric device that rotates its rotor shaft in one direction or in two directions. The fan is made more effective by its being designed with two sets of blades, where each set of blades draws in cooling air to the dynamoelectric device from the axially opposite ends of the device.
As with conventional straight blade radial fans, the two sided radial fan of the invention is provided with a center hub that connects the fan to the shaft of the dynamoelectric device at one of the axially opposite ends of the device. Extending radially outward from the hub are a first plurality of blades and a second plurality of blades that are positioned on axially opposite sides of the fan. The fan is mounted on the dynamoelectric device shaft with the second plurality of blades adjacent the device and with the first plurality of blades positioned on the axially opposite side of the second plurality of blades from the device.
A radially oriented plate having axially opposite first and second surfaces separates the first plurality of blades from the second plurality of blades. The plate has a circular perimeter edge and a circular inner edge adjacent the fan hub. The first plurality of blades extend radially straight across the first surface of the plate to distal ends of the blades that are spaced radially outward from the plate perimeter edge. The second plurality of blades extend radially straight across the second surface of the plate to distal ends of the blades spaced radially outward from the plate perimeter edge. The distal ends of the first plurality of blades are angled relative to the fan axis of rotation and merge with the distal ends of the second plurality of blades.
An annular ring connects the second plurality of blades adjacent their distal ends. Because the distal ends of the second plurality of blades extend radially outward from the plate perimeter edge, the annular ring is also spaced radially outward from the plate perimeter edge. The annular ring has an oblique cross section relative to the axis of rotation of the fan and tapers or angles radially outward from the axis of rotation as the ring extends axially away from the first plurality of blades.
Because the two sided radial fan of the invention can operate in two directions of rotation, it advantageously can be mounted to the shaft of the dynamoelectric device at either axial end of the device. On rotation of the fan by the shaft of the device, the first plurality of blades function as straight radial fan blades forcing a flow of air centrifugally from the center of the fan radially outward along the blades toward the blade distal ends. This creates a vacuum at the center of the fan that draws an axial flow of air in a first direction into the fan toward the fan first surface. The radial flow of air toward the distal ends of the first plurality of blades is first directed against the interior surface of the electromotive device housing, and is then directed by the interior surface to flow axially through the housing from the end of the housing with the fan to the axially opposite end of the housing, thereby cooling the electromotive device at its exterior.
The rotation of the fan by the shaft of the electromotive device also causes the second plurality of blades to centrifugally force air radially outward toward the distal ends of the blades. This creates a vacuum at the center of the fan adjacent the fan second surface. This vacuum draws air axially into the electromotive device from the end of the device axially opposite the fan. This cooling air is drawn through the center of the electromotive device to the vacuum created at the center of the second surface of the fan plate. The air drawn through the electromotive device to the center of the plate second surface is then pushed radially outward along the second plurality of fan blades. This flow of air is directed toward the interior surface of the annular ring connecting the second plurality of blades. The annular ring interior surface redirects the flow of air in an axially opposite direction out over the stator windings of the electromotive device, thereby further cooling the electromotive device. Thus, the radial flow of air created by the fan is split with a first portion of the air flow pushed by the first plurality of blades being redirected by the end shield interior surface to flow axially over the exterior of the electromotive device and a second portion of the air flow pushed by the second plurality of blades being redirected by the annular ring to flow axially over the stator windings of the device to thereby cool the device.
In the manner described above, the two sided radial fan of the invention draws cooling air into the electromotive device from the axially opposite ends of the electromotive device, where in prior art cooling fans cooling air is only drawn into one of the axially opposite ends of the electromotive device. By drawing cooling air into both of the axially opposite ends of the electromotive device, the two sided radial fan of the invention provides greater cooling efficiency to the electromotive device without significantly increasing the size of the fan or the device and without significantly increasing the cost or adding additional components to the electromotive device construction.